Generally, a boom and an arm of an excavator may be operated by a flux. The flux may be transferred to the boom and the arm from a hydraulic pump through a main control valve. A recent excavator may include a first hydraulic pump and a second hydraulic pump. Thus, the main control valve may include first and second boom control spools arranged between the first and second hydraulic pumps and a boom cylinder, and first and second arm control spools arranged between the first and second hydraulic pumps and an arm cylinder.
According to related arts, when the boom or the arm may be separately operated, a first flux generated from the first hydraulic pump and a second flux generated from the second hydraulic pump may be supplied to the boom cylinder or the arm cylinder through the first and second boom control spools or the first and second arm control spools.
When the boom and the arm may be simultaneously operated, the first flux may be partially supplied to the arm cylinder through the second arm control spool and the second flux may be partially supplied to the boom cylinder through the second boom control spool.
Therefore, when the boom and the arm may be simultaneously operated, a part of the first flux may pass through the second arm control spool and a part of the second flux may pass through the second boom control spool so that pressure loss may be generated.